I can do both a GP 30 and a B30 (couldn't do two Bs though, at least not in the same year !!)I have the GP30 in blue Zanzibar and a Feu B30! The GP30 will give you a good indication of size. Between the two, I find the GP to be more relaxed and easy going. Depending on where you go it can be more under the radar than a B.
But if you have your heart set on a B and can’t get both, I would keep waiting! Don’t settle just because you can get it now.
I am thinking I might get the GP30 because I do like it (In general, I do like the GP; I have a GP 36 that I used constantly last summer) and I can definitely see myself using it now. I like that it is easy and carefree, I'd be using it to go to my son's baseball games, or for shopping or for just hanging out; who knows, maybe even for work. I currently use a B35, so getting the smaller GP will also let me know how well the smaller 30 size actually works for me. Plus, I like the idea of getting the GP for a pop of color but getting the B30 in a classic color.